In a known web printing system, an ink is printed on a web media to form an image on a print area of the web. The printing system comprises a supply roller for supplying the web from a roll to a transport pinch, which is configured for moving the web through a transport path in a transport direction along a print unit for printing the ink onto the web to form the image. During printing of the ink onto the web, the ink will solidify on the web.
In a known printing method a leading edge of the web is first fed from the supply roll towards the transport pinch. The transport pinch engages the web to drive the web along the transport path. The transport pinch is arranged near the print unit along the transport path for accurately controlling the web, when it moves along the print unit.
In case the printing system is not printing on the web, the printing system switches to a ready-to-print mode. In the ready-to-print mode, the web is maintained stationary by the transport pinch, such that the web is ready to be printed on directly after the ready-to-print mode, i.e. is enabled to start printing without delay for preparing one or more parts or modules of the printing system for printing.
When the printing system after the ready-to-print mode switches to a printing mode to print a next image onto the web, the web is moved by the transport pinch through the transport path along the print unit and the print unit starts printing the image onto a print area of the web. The print area is an area of the web, on which an image—in this case after the ready-to-print mode in particular a next image—may be printed.
In case the web is maintained stationary by the transport pinch over a longer period of time in the ready-to-print mode, a deformation of the web in the form of pressure marks may occur in the web at the position of the transport pinch. Especially a pressure sensitive web material may be deformed at the transport pinch.
In another example, the printing system further comprises a pre-heat unit for heating the web in a heating zone upstream of the print unit relative to the transport direction. The transport path of the web, which is controlled by the transport pinch, comprises the heating zone.
In case the web is maintained stationary over a longer period of time in the ready-to-print mode, a deformation of the web may occur in the web in the heating zone, due to the heat applied by the pre-heat unit to the stationary web in the heat zone, such as deformation in the form of shrinkage of the web in a width direction due to evaporation of water from the web material.
When the web is deformed during the ready-to-print mode, a printing of the ink on the print area of the web may fixate said deformation of the web as the ink solidifies on the web during the printing step. As a result, a permanent deformation of the web and of the image on the web may occur, which deteriorates the quality of the printed image.
In any of these examples, in a web deformation position along the transport path the web may be deformed in the ready-to-print mode in case the web is exposed to web deformation conditions over a longer period. Said deformation of the web may be relatively persistent in that the deformation will only slowly recover. When the web is exposed to a web deformation condition, such as a pressure in a transport pinch, for only a short period, substantially no deformation of the web will occur or the deformation may substantially instantly recover.
Retracting the web from the transport path back to the supply roll and away from the transport assembly may prevent a deformation of the web, which deformation would occur in response to a longer period in the ready-to-print mode. However, in that case the web is not ready to be printed on, as the web is removed from the transport path and is rewound on the supply roll.
U.S. Pat. No. 5,351,071A describes a thermal printer of the type printing an image on a printing paper wound in the form of a roll. Curling of the printing paper wound in the roll form occurs when the thermal printer is placed in its standby mode over more than a predetermined period of time while the printing paper is held between a platen roller and a thermal head. In order to prevent curling of the printing paper, the printing paper is rewound when the standby mode lasts over more than the predetermined period of time
It is an object to provide a method for controlling a web in a printing apparatus, wherein the method prevents deformation of a print area of the web in a ready-to-print mode, in which mode said web is ready to be printed an image onto directly after the ready-to-print mode.